A method is provided for controlling braking in a vehicle having a motor and a brake. The method includes sensing an actual operating parameter of the motor and receiving a desired operating parameter of the motor. The motor is controlled based on the actual operating parameter and the desired operating parameter of the motor. The brake is controlled based on the actual operating parameter and the desired operating parameter of the motor and an output from the motor control.
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1. A method for controlling braking in a vehicle having a motor and a brake, comprising:
determining an operating mode of the motor from a motor speed and a motor torque;
sensing an actual operating parameter of the motor;
receiving a desired operating parameter of the motor;
controlling the motor based on the actual operating parameter and the desired operating parameter of the motor if the determined operating mode of the motor is a retarding mode; and
controlling the brake based on the actual parameter and the desired parameter of the motor and an output from the motor control if the determined operating mode of the motor is the retarding mode.
15. A system for controlling braking in a vehicle having a motor and a brake, comprising:
a motor operating parameter sensor;
an operator input unit; and
a control unit coupled to the motor operating parameter sensor and the operator input unit, the control unit being configured to determine whether the motor is in a retarding mode based on a motor speed and a motor torque, the control unit including:
a motor controller configured to determine a motor control output to control the motor based on signals from the motor operating parameter sensor and the operator input unit if the determined operating mode of the motor is the retarding mode; and
a brake controller coupled to the motor controller, the motor operating parameter sensor, and the operator input unit, the brake controller being configured to determine a brake control output to control the brake based on the signals from the motor operating parameter sensor, the operator input unit, and the motor control output if the determined operating mode of the motor is the retarding mode.
28. A vehicle, comprising:
a motor;
a transmission unit coupled to the motor, the transmission unit having a brake;
a drive train coupled to the transmission unit;
an operator input;
a motor operating parameter sensor;
a control unit coupled to the operator input and the motor operating parameter sensor, the control unit being configured to determine whether the motor is in a retarding mode based on a motor speed and a motor torque, the control unit including:
a motor controller configured to determine a motor control output to control the motor based on signals from the motor operating parameter sensor and the operator input unit if the determined operating mode of the motor is the retarding mode; and
a brake controller coupled to the motor controller, the motor operating parameter sensor, and the operator input unit, the brake controller being configured to determine a brake control output to control the brake based on the signals from the motor operating parameter sensor, the operator input unit, and the motor control output if the determined operating mode of the motor is the retarding mode.
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The present disclosure is directed to a system and method for controlling braking in a vehicle. More particularly, the disclosure relates to a system and method for controlling braking in an electric drive vehicle.
In an earth-moving machine or vehicle, such as an excavator or a loader, brakes perform important functions. Brakes are used for power management in a vehicle, including an electric drive vehicle. Typically, an electric drive vehicle has an electric motor that propels the vehicle and a brake that slows down the vehicle. By engaging the brake, the vehicle can slow down quickly, for example, to avoid an obstacle or change its moving direction. Thus, earth-moving vehicles need a brake for safety as well as their operating efficiency.
Under certain operating conditions, the vehicle is operated in a retarding or regenerating mode. Typically, retardation or regeneration occurs when the vehicle slows down from its present speed or the vehicle is pulled due to the gravity. The vehicle may experience the retarding mode, for example, when it goes down a steep hill. In such instances, the vehicle needs to dissipate energy to slow down or maintain its speed. If the vehicle does not dissipate or absorb energy when going down a steep slope, then the vehicle simply accelerate to faster and faster speeds. Similarly, the vehicle needs to dissipate or absorb energy to slow down.
In the retarding mode, the brake is often used to dissipate extra energy or power for better vehicle performance and safety. While a brake is an important part of any earth-moving vehicle, it should not unnecessarily interfere with the vehicle performance. For example, the brake control should not interfere with a motor speed control before the motor power limitation is reached. Also, brake control should provide stability to the operation of the vehicle.
Some attempts have been made to provide such braking control. For example, U.S. Pat. No. 6,551,212 discloses a decelerator system for a work machine. The deceleration system has a machine control device including an engine control, a transmission control, and a brake control. The machine control device receives an engine control signal, a transmission control signal, and a brake control signal. While the decelerator system disclosed in U.S. Pat. No. 6,551,212 provides a good system to decelerate a vehicle, a brake control system that provides automatic, integrated control of the motor and brake is desired. It is further desirable to provide an automatic brake control system that has more robust stability and does not sacrifice vehicle performance. It is also desirable to provide an integrated motor/brake control system that can handle system uncertainties with excellent stabilities.
Thus, the present brake control system is directed to solving one or more of the shortcomings associated with prior art designs and providing a braking control system with more stability and less interference with the vehicle performance.
In one aspect, a method is provided for controlling braking in a vehicle having a motor and a brake. The method includes sensing an actual operating parameter of the motor and receiving a desired operating parameter of the motor. The motor is controlled based on the actual operating parameter and the desired operating parameter of the motor. The brake is controlled based on the actual operating parameter and the desired operating parameter of the motor and an output from the motor control.
In another aspect, a system is provided for controlling braking in a vehicle having a motor and a brake. The system includes a motor operating parameter sensor and an operator input unit. A control unit is coupled to the motor operating parameter sensor and the operator input unit. The control unit includes a motor controller configured to determine a motor control output to control the motor based on signals from the motor operating parameter sensor and the operator input unit. A brake controller is coupled to the motor controller, the motor operating parameter sensor, and the operator input unit. The brake controller is configured to determine a brake control output to control the brake based on the signals from the motor operating parameter sensor, the operator input unit, and the motor control output.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description, serve to explain the principles of the invention.
Reference will now be made in detail to exemplary embodiments that are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
The brakes 22 are attached to shafts in the transmission unit 14 to provide a retarding torque for the vehicle. Each of the brakes 22 is controlled by a hydraulic pressure valve 23, which is controlled by the control unit 18 (a connection to only one pair is shown in the figure). In this embodiment, a signal, such as an electric current, is sent from the control unit 18 to the valve 23. The valves 23 allow the brakes 23 to provide control pressure corresponding to the signal. The pressure control valves 23 are controlled by an electric current that can be regulated by the control unit 18. The relationship between the valve control current and the control pressure of the brakes 22 may be linearly or nonlinearly mapped depending on dynamic features of the valves 23. In most cases, if the pressure control valve 23 is a linear system, a first order transfer function is adequate to represent the mapping between the control current input and the control pressure output.
The retarding torque is generated in proportion to the friction between brake disks. The friction and the brake control pressure are assumed to be in either a linear or nonlinear relationship, and the brake control pressure can be assumed to control the retarding torque that the brakes 22 produce.
The control unit 18 is coupled to an operator input unit 28 and a motor operating parameter sensor 30. In one embodiment, the operator input unit 28 may be a lever that an operator of the vehicle moves to drive the vehicle, and the motor operating parameter sensor 30 may be a motor speed sensor. The motor speed sensor 30 may be a transducer that can measure the rotational speed of the motor 12, but any other sensor that is known for measuring motor speed may be used.
In addition to the motor speed sensor 30, the vehicle 10 may include a motor torque sensor 29 for measuring a torque of the motor 12. While the motor torque sensor 29 is not described here in detail, it can be any type of sensor that is known for sensing a motor torque. For example, the motor torque sensor 29 may be a motor control current sensor. By measuring the motor control current, the motor toque may be readily obtained.
In one embodiment, the brake control system should only be activated when the motor 12 is in a retarding mode. The control unit 18 may determine whether the motor 12 is operating in the retarding mode. The motor is in the retarding mode, for example, when a multiplication value of the sensed motor speed and the sensed motor toque is less than zero.
Also, the brake control system should not interfere with the normal operation of the motor 12. When the motor power or torque is below a motor torque limit at the sensed motor speed, the system should not be activated. Typically, the motor power limit value is decided based on a particular motor. Thus, a different motor may have a different motor power limit value at a particular motor speed.
As illustrated in
The operator of the vehicle operates the operator input unit 28 and sends a desired motor speed signal, ωd. The motor operating parameter sensor 30 is a motor speed sensor (not shown in the figure) that senses an actual motor speed and sends a motor speed signal, ωm.
In the embodiment shown in
The motor controller 32 determines a motor control torque, Tc, based on the modified value sent from the modifier 39. While the motor controller 32 is a proportional-integral-derivative (PID) controller in this embodiment, it can be any other type of controller that is suitable to determine the motor control torque Tc from the modified value.
The motor control torque Tc from the motor controller 32 is sent to the motor torque-current converter 38. The motor torque-current converter 38 may include an equation or a map that defines a torque-current relationship of the motor 12 and determines a motor control current, Im, from the motor control torque Tc. The torque-current relationship of the motor 12 may be linear or nonlinear. The relationship of a particular motor may be empirically determined by testing the motor.
Once the converter 38 determines the motor control current Im corresponding to the motor control torque, the motor control current is forwarded to the motor 12. In response, the motor 12 provides the motor speed corresponding to the motor control current Im.
As shown in
In the exemplary embodiment of
The brake control torque Tb from the brake control 34 is forwarded to the modifier 41. In this embodiment, the brake control torque Tb is modified by adding the output from the upper transmission part 40 at the modifier 41. The added value is then sent to the brakes 22 via brake pressure valves so that the corresponding brake pressure is applied by the brakes 22 to retard the vehicle. As a result of the applied brake pressure, the disk of the brakes 22 rotate at a rotational speed of ωb.
The brake rotational speed ωb is transmitted to a brake-sprocket (lower) part 42 of the transmission unit 14. Once various vehicle loads that the vehicle 10 is exposed to during its operation are taken into account, the velocity, Vv, of the vehicle 10 is output from the lower transmission part 42.
In this exemplary embodiment, the brake rotational speed ωb is also transmitted to a multiplier 44. At the multiplier 44, the brake rotational speed ωb is multiplied by the brake control torque Tb from the brake controller 34. As a result of the multiplication (Tb*ωb), a brake power is obtained and sent to a modifier 46. At the modifier 46, this brake power output from the multiplier 44 is subtracted from a brake power limit, Powb, lim. The brake power limit Powb, lim should be set at the point which the power dissipated by the brakes exceeds their limit. When the absolute value of Tb*ωb is determined to have exceeded the brake power limit, the difference between the absolute value of Tb*ωb and the brake power limit is determined at the brake power controller 36.
The brake power controller 36 determines a value of the motor speed modification signal δ107 d based on the difference between the value of Tb*ωb and the brake power limit. The brake power controller 36 may be a PID controller or any other controller known to one skilled in the art to be suitable to determine the motor speed modification signal δωd. In the embodiment shown in
By Newton's law,
Tc−Tbm/Nmb=Jm{acute over (ω)}m+cmωm
Tb+Tbm=k/Nbs∫(ωm/Ntr−ωs)dt, where the transmission inertia is neglected.
−T1=Jv{acute over (ω)}s+csωs+k∫(ωs−ωm/Ntr)dt
By Laplace transform, assuming zero initial conditions for all the integral terms, we have
Tc(s)−Tbm(s)/Nmb=(Jms+cm)ωm(s)
Tb(s)+Tbm(s)=k/sNbs[ωm(s)/Ntr−ωs(s)]
−T1(s)=(Jvs+cs)ωs(s)+k/s[ωs(s)−ωm(s)/Ntr]
Further,
ωm(s)={Ntr2(Jvs2+css+k)[Tb(s)/ Nmb+Tc(s)]−kNtrT1(s)}/{JmNtr2Jvs3+Ntr2(Jmcs+Jvcm)s2+(kJmNtr2+kJv+Ntr2cmcs)s+k(cs+Ntr2cm)2}
Then the control logic of the brake control system can be illustrated as in
P(s)=Ntr2(Jvs2+css+k)/{JmNtr2Jvs3+Ntr2(Jmcs+Jvcm)s2+(kJmNtr2+kJv+Ntr2cmcs)s+k(cs+Ntr2cm)2}
D(s)=k/[Ntr(Jvs2+css+k)]
Based on the above-described analysis and
In the embodiment in
A relationship between the motor speed and the brake control pressure is plotted in
When the desired motor speed is ωd(t) and the power limit on the brakes is W1, the modified motor speed signal ωd′ is determined as:
ωd′=ωd(t), if Pbωm<kwW1
ωd′=kwW1/Pb, if Pbωm≧kwW1, where kw is a constant related to the brake-motor transmission ratio and other parameters. In one embodiment, a low-pass filter or a boundary control may be added to prevent the control system from chattering.
In the other approach, the desired motor speed ωd may be modified by adding δωd, as illustrated in
ωd′=ωd−δωd=ωd−f(kwW1−Pbωm,t),
where f(,) is a globally bounded dynamic mapping depending on the error of the brake power. Thus,
δωd=0, if Pbωm<kwW1
δωd=kbpp(kwW1−Pbωm)+∫(kwW1−Pbωm)dt, if Pbωm≧kwW1
Referring to
Second, the control system senses the motor control toque Tc to see if it is beyond the motor torque limit of the motor 12 at the motor speed ωm. When the motor 12 is operating in the retarding mode and the motor control torque exceeds the motor torque limit at the motor speed, the brake control system may be activated. By providing these two conditions for activation, the brake control should not interfere with the motor speed control within its normal operation range.
Once the brake control is activated, it provides automatic, integrated control over the motor and the brakes according to the operation of the one embodiment described in the above section.
The automatic vehicle brake control are activated under the motor retarding mode with a motor power limit. Also, in one embodiment, the brake control provides a stable, closed-loop control scheme to provide a certain brake control pressure for regulating the vehicle speed to track its desired trajectory within the brake power limit.
It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed system and method without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims.
Du, Hongliu, Kuras, Brian D., Sopko, Thomas M., Stemler, Eric D., Barngrover, Michael J., Pandey, Saurabh
Patent | Priority | Assignee | Title |
10960889, | Mar 05 2018 | ZF Friedrichshafen AG | Gear-shifting method for an electric drive system |
Patent | Priority | Assignee | Title |
6551212, | Feb 16 2001 | Caterpillar Inc | Decelerator system for a work machine |
6816768, | Aug 31 2000 | Nissan Motor Co., Ltd. | Controlling scheme for stand-by braking torque applied to automotive vehicle |
6986727, | Dec 23 2003 | Caterpillar Inc. | Retarding control for an electric drive machine |
7001306, | Feb 18 2003 | Nissan Motor Co., Ltd. | Brake control apparatus |
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